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  • richardmitnick 3:25 pm on November 19, 2014 Permalink | Reply
    Tags: , , Quantum Mechanics   

    From livescience: “Parallel Worlds Could Explain Wacky Quantum Physics” 

    Livescience

    November 19, 2014
    Kelly Dickerson

    The idea that an infinite number of parallel worlds could exist alongside our own is hard to wrap the mind around, but a version of this so-called Many Worlds theory could provide an answer to the controversial idea of quantum mechanics and its many different interpretations.

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    Credit: Shutterstock/Juergen Faelchle

    Bill Poirier, a professor of physics at Texas Tech University in Lubbock, proposed a theory that not only assumes parallel worlds exist, but also says their interaction can explain all the quantum mechanics “weirdness” in the observable universe.

    Poirier first published the idea four years ago, but other physicists have recently started building on the idea and have demonstrated that it is mathematically possible. The latest research was published Oct. 23 in the journal Physical Review X.

    Quantum mechanics is the branch of physics that describes the rules that govern the universe on the microscopic scale. It tries to explain how subatomic particles can behave as both particles and as waves. It also offers an explanation about why particles appear to exist in multiple positions at the same time.

    This fuzzy clump of possible positions is described by a “wave function” — an equation that predicts the many possible spots a given particle can occupy. But the wave function collapses the second anyone measures the actual position of the particle. This is where the multiverse theory comes in.

    Some physicists believe that once a particle’s position is measured, the many other positions it could take according to its wave function split off and create separate, parallel worlds, each only slightly different from the original.

    Hugh Everett was the first physicist to propose the possibility of a multiverse — an infinite number of parallel universes that exist alongside our own. He published his Many Worlds theory in the 1950s, but the idea was not well-received in the academic world.

    Everett ended his career in physics shortly after getting his Ph.D., but many physicists now take the multiverse and parallel-worlds idea seriously. Poirier reworked the Many Worlds theory into the less abstract Many Interacting Worlds (MIW) theory, which could help explain the weird world of quantum mechanics.

    Quantum mechanics has existed for more than a century, but its interpretation is just as controversial today as it was 100 years ago, Poirier wrote in his original paper.

    Albert Einstein was not a fan of quantum mechanics. The idea that a particle could exist in a haze of probability instead of a definite location did not make sense to him, and he once famously said, “God does not play dice with the universe.” However, this new MIW theory might have helped to put Einstein’s mind at ease. In the MIW theory, quantum particles don’t act like waves at all. Each parallel world has normal-behaving particles and physical objects. The wave-function equation doesn’t have to exist at all.

    In the new study, which builds on Poirier’s idea, physicists from Griffith University in Australia and the University of California, Davis, demonstrate that it only takes two interacting parallel worlds — not an infinite number — to produce the weird quantum behavior that physicists have observed. Neighboring worlds repulse one another, the researchers wrote in the paper. This force of repulsion could explain bizarre quantum effects, such as particles that can tunnel through barriers.

    But how can physicists prove we’re living in just one of millions of other worlds, or that these worlds interact? Poirier thinks it will take some time to develop a way to test the idea.

    “Experimental observations are the ultimate test of any theory,” Poirier said in a statement. “So far, Many Interacting Worlds makes the same predictions as standard quantum theory, so all we can say for sure at present is that it might be correct.”

    The authors of the new paper hope that expanding the MIW theory will lead to ways to test for parallel worlds and further explain quantum mechanics.

    Richard Feynman, a physicist who worked on the Manhattan Project, once said, “I think I can safely say that nobody understands quantum mechanics,” but Poirier and his colleagues argue that physicists have much to gain from trying.

    See the full article here.

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  • richardmitnick 6:16 am on November 17, 2014 Permalink | Reply
    Tags: , , , Quantum Mechanics   

    From NYT: “Is Quantum Entanglement Real?” 

    New York Times

    The New York Times

    NOV. 14, 2014
    SundayReview
    DAVID KAISER

    FIFTY years ago this month, the Irish physicist John Stewart Bell submitted a short, quirky article to a fly-by-night journal titled Physics, Physique, Fizika. He had been too shy to ask his American hosts, whom he was visiting during a sabbatical, to cover the steep page charges at a mainstream journal, the Physical Review. Though the journal he selected folded a few years later, his paper became a blockbuster. Today it is among the most frequently cited physics articles of all time.

    man

    Bell’s paper made important claims about quantum entanglement, one of those captivating features of quantum theory that depart strongly from our common sense. Entanglement concerns the behavior of tiny particles, such as electrons, that have interacted in the past and then moved apart. Tickle one particle here, by measuring one of its properties — its position, momentum or “spin” — and its partner should dance, instantaneously, no matter how far away the second particle has traveled.

    The key word is “instantaneously.” The entangled particles could be separated across the galaxy, and somehow, according to quantum theory, measurements on one particle should affect the behavior of the far-off twin faster than light could have traveled between them.

    Entanglement insults our intuitions about how the world could possibly work. Albert Einstein sneered that if the equations of quantum theory predicted such nonsense, so much the worse for quantum theory. “Spooky actions at a distance,” he huffed to a colleague in 1948.

    In his article, Bell demonstrated that quantum theory requires entanglement; the strange connectedness is an inescapable feature of the equations. But Bell’s proof didn’t show that nature behaved that way, only that physicists’ equations did. The question remained: Does quantum entanglement occur in the world?

    Starting in the early 1970s, a few intrepid physicists — in the face of critics who felt such “philosophical” research was fit only for crackpots — found that the answer appeared to be yes.

    John F. Clauser, then a young postdoctoral researcher at the Lawrence Berkeley National Laboratory, was the first. Using duct tape and spare parts, he fashioned a contraption to measure quantum entanglement. Together with a graduate student named Stuart Freedman, he fired thousands of pairs of little particles of light known as photons in opposite directions, from the middle of the device, toward each of its two ends. At each end was a detector that measured a property of the photon known as polarization.

    As Bell had shown, quantum theory predicted certain strange correlations between the measurements of polarization as you changed the angle between the detectors — correlations that could not be explained if the two photons behaved independently of each other. Dr. Clauser and Mr. Freedman found precisely these correlations.

    Other successful experiments followed. One, led by the French physicist Alain Aspect, tested the instantaneousness of entanglement. Another, led by the Austrian physicist Anton Zeilinger, considered entanglement among three or more particles.

    Even with these great successes, work remains to be done. Every experimental test of entanglement has been subject to one or more loopholes, which hold out the possibility, however slim, that some alternative theory, distinct from quantum theory and more in line with Einstein’s intuitions, may still be salvageable. For example, one potential loophole — addressed by Dr. Aspect’s experiment — was that the measurement device itself was somehow transmitting information about one particle to the other particle, which would explain the coordination between them.

    The most stubborn remaining loophole is known as “setting independence.” Dr. Zeilinger and I, working with several colleagues — including the physicists Alan H. Guth, Andrew S. Friedman and Jason Gallicchio — aim to close this loophole, a project that several of us described in an article in Physical Review Letters.

    HERE’S the problem. In any test of entanglement, the researcher must select the settings on each of the detectors of the experimental apparatus (choosing to measure, for example, a particle’s spin along one direction or another). The setting-independence loophole suggests that, though the researcher appears to be free to select any setting for the detectors, it is possible that he is not completely free: Some unnoticed causal mechanism in the past may have fixed the detectors’ settings in advance, or nudged the likelihood that one setting would be chosen over another.

    Bizarre as it may sound, even a minuscule amount of such coordination of the detectors’ settings would enable certain alternative theories to mimic the famous predictions from quantum theory. In such a case, entanglement would be merely a chimera.

    How to close this loophole? Well, obviously, we aren’t going to try to prove that humans have free will. But we can try something else. In our proposed experiment, the detector setting that is selected (say, measuring a particle’s spin along this direction rather than that one) would be determined not by us — but by an observed property of some of the oldest light in the universe (say, whether light from distant quasars arrives at Earth at an even- or odd-numbered microsecond). These sources of light are so far away from us and from one another that they would not have been able to receive a single light signal from one another, or from the position of the Earth, before the moment, billions of years ago, when they emitted the light that we detect here on Earth today.

    That is, we would guarantee that any strange “nudging” or conspiracy among the detector settings — if it does exist — would have to have occurred all the way back at the Hot Big Bang itself, nearly 14 billion years ago.

    If, as we expect, the usual predictions from quantum theory are borne out in this experiment, we will have constrained various alternative theories as much as physically possible in our universe. If not, that would point toward a profoundly new physics.

    Either way, the experiment promises to be exciting — a fitting way, we hope, to mark Bell’s paper’s 50th anniversary.

    See the full article here.

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  • richardmitnick 3:54 pm on November 4, 2014 Permalink | Reply
    Tags: , , , Quantum Mechanics   

    From MIT: “Doctoral students seek quantum control in Paola Cappellaro’s Quantum Engineering Group” 


    MIT News

    November 4, 2014
    Peter Dunn | Nuclear Science & Engineering

    MIT’s Quantum Engineering Group (QEG) has a challenging but potentially world-changing mission: to harness the quantum properties of matter for use in information technology, metrology, defense, healthcare, and many other fields.

    The interdisciplinary laboratory, headed by Department of Nuclear Science and Engineering (NSE) Associate Professor Paola Cappellaro, is working theoretically and experimentally towards achieving quantum control — the ability to control and utilize the behavior of nanoscale particles, which obey the laws of quantum mechanics rather than classical physics. A close-knit group of student researchers plays a central role, developing basic enabling tools that could yield dividends for decades to come.

    “In one sense we’re doing fundamental research, but it’s really engineering — we’re seeking practical applications,” explains Cappellaro. The QEG is based in MIT’s Research Lab of Electronics, which brings together faculty and students from many departments (including NSE, physics, materials science, and electrical engineering and computer science) and other quantum-oriented programs at the Institute.

    “Everyone’s working from different directions, but the common goal is to get control of quantum systems and be able to exploit them to build quantum devices,” says Cappellaro. “The common theme is using nitrogen-vacancy (NV) centers in diamonds as a promising experimental platform for this goal.” NV centers, a type of crystal defect, allow access to nearby electrons and their intrinsic angular momentum, or spin.

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    Graduate students Alexandre Cooper-Roy (left), Masashi Hirose (center), and Ashok Ajoy work to harness the quantum properties of matter in MIT’s Quantum Engineering Group. Photo: Susan Young

    Applications could include leveraging spin to create quantum bits (qubits) for information processing and storage, which would provide exponential increases in computing power, and using NV-containing diamonds as ultra-responsive sensors, able to map molecular structures or monitor nano-scale magnetic fields like those created by brain functions.

    There are many hurdles. One is that spin cannot be completely isolated, and is subjected to deleterious noise. This can lead to the decay of quantum superposition, or decoherence, which represents one of the major challenges to quantum control.

    Doctoral student Masashi Hirose hopes to help solve the decoherence problem by learning how to use the electronic spin of NV centers to control the spin of nearby atomic nuclei (nuclear spin). “The nuclear spin is much harder to control directly than the electronic spin, but it’s more resistant to noise and can stay in a superposition state for milliseconds rather than microseconds, a 1,000 times increase,” explains Hirose. “The nuclear spin can act as an auxiliary qubit to protect the electronic spin from decoherence.”

    Thus, the nuclear spin is a good candidate for memory functions in quantum computing, while computation could be handled with the electronic spin. Development of a control theory for interactions between the two is a research priority for Hirose, who joined Cappellaro’s lab group in 2009 after undergraduate work in Japan.

    “The subject matter is a dream for me, and the QEG environment is very cooperative, everyone shares their problems,” he says. “I meet with Paola at least every couple of days, and she always welcomes new ideas, and helps figure out next steps.”

    Fellow doctoral student Alexandre Cooper-Roy is also focused on leveraging the NV center electronic spin, and extending today’s rudimentary control abilities to create quantum resources, like multiple-qubit computing structures or sensors.

    “NV centers are interesting because we can use them to control and read out the electronic spins associated with other impurities in the diamond lattice,” says Cooper-Roy. “Now we’d like to be able to put a few of these objects together so that we can do things that aren’t currently accessible, but the dynamics become really complicated.”

    Cooper-Roy, who has studied in Japan and France as well as his native Canada, notes that the QEG’s research approach emphasizes work at room temperature using relatively simple equipment, which makes it possible for individuals to manage projects.

    “A student can come here and build an experiment from scratch; it’s an easy test bed for exploration of quantum mechanics,” he says. “It’s great for training and for seeking practical applications. MIT is a great experience, because there’s an engineering approach — people really focus on optimizing the process. The final product is very important.”

    Meanwhile, another PhD candidate, Ashok Ajoy, is attacking the problem of using quantum sensor technology as a sub-molecular microscope. “We’d like to be able to determine the structure of biomolecules, like proteins,” he explains. “The structure and the function are closely tied, and this would enable, say, the design of antibiotics, or the ability to block or amplify what a molecule does.”

    The current goal is to achieve resolution of a few angstroms, which requires a synergistic combination of theory and experimentation. “In our lab we do both; I like it that way,” he says, adding that Cappellaro’s personal mentorship is an important enabler.

    Long term, there is the potential to achieve sensing at resolution of a single spin: “That’s the holy grail; no one has been able to measure single external nuclear spins and map out their positions,” says Ajoy, who did his undergraduate studies in India. “With these sensors that we and our community have we’re on the cusp; it’s an exciting threshold, a stepping stone to something that could be very useful going forward in all sorts of applications.”

    That broad applicability has attracted funding from blue-chip sources, like the National Science Foundation and the Department of Defense. “All the work is fundamentally enabling,” says Cappellaro. “We develop the tools we use in order to create better devices, but also seek to understand the physics so we can come up with smarter ways to use them.”

    See the full article here.

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  • richardmitnick 6:18 pm on October 28, 2014 Permalink | Reply
    Tags: , , , Quantum Mechanics   

    From Brown: “Can the wave function of an electron be divided and trapped?” 

    Brown University
    Brown University

    October 28, 2014
    Kevin Stacey 401-863-3766

    Electrons are elementary particles — indivisible, unbreakable. But new research suggests the electron’s quantum state — the electron wave function — can be separated into many parts. That has some strange implications for the theory of quantum mechanics.

    New research by physicists from Brown University puts the profound strangeness of quantum mechanics in a nutshell — or, more accurately, in a helium bubble.

    Experiments led by Humphrey Maris, professor of physics at Brown, suggest that the quantum state of an electron — the electron’s wave function — can be shattered into pieces and those pieces can be trapped in tiny bubbles of liquid helium. To be clear, the researchers are not saying that the electron can be broken apart. Electrons are elementary particles, indivisible and unbreakable. But what the researchers are saying is in some ways more bizarre.

    tank
    The electron wave function A canister of liquid helium inside the blue cylinder allowed researchers to experiment with tiny electron bubbles only 3.6 nanometers in diameter. The work suggests that the wave function of an electron can be split and parts of it trapped in smaller bubbles. Photo: Mike Cohea/Brown University

    In quantum mechanics, particles do not have a distinct position in space. Instead, they exist as a wave function, a probability distribution that includes all the possible locations where a particle might be found. Maris and his colleagues are suggesting that parts of that distribution can be separated and cordoned off from each other.

    “We are trapping the chance of finding the electron, not pieces of the electron,” Maris said. “It’s a little like a lottery. When lottery tickets are sold, everyone who buys a ticket gets a piece of paper. So all these people are holding a chance and you can consider that the chances are spread all over the place. But there is only one prize — one electron — and where that prize will go is determined later.”

    If Maris’s interpretation of his experimental findings is correct, it raises profound questions about the measurement process in quantum mechanics. In the traditional formulation of quantum mechanics, when a particle is measured — meaning it is found to be in one particular location — the wave function is said to collapse.

    “The experiments we have performed indicate that the mere interaction of an electron with some larger physical system, such as a bath of liquid helium, does not constitute a measurement,” Maris said. “The question then is: What does?”

    And the fact that the wave function can be split into two or more bubbles is strange as well. If a detector finds the electron in one bubble, what happens to the other bubble?

    “It really raises all kinds of interesting questions,” Maris said.

    The new research is published in the Journal of Low Temperature Physics.

    Electron bubbles

    Scientists have wondered for years about the strange behavior of electrons in liquid helium cooled to near absolute zero. When an electron enters the liquid, it repels surrounding helium atoms, forming a bubble in the liquid about 3.6 nanometers across. The size of the bubble is determined by the pressure of the electron pushing against the surface tension of the helium. The strangeness, however, arises in experiments dating back to the 1960s looking at how the bubbles move.

    In the experiments, a pulse of electrons enters the top of a helium-filled tube, and a detector registers the electric charge delivered when electron bubbles reach the bottom of the tube. Because the bubbles have a well-defined size, they should all experience the same amount of drag as they move, and should therefore arrive at the detector at the same time. But that’s not what happens. Experiments have detected unidentified objects that reach the detector before the normal electron bubbles. Over the years, scientists have cataloged 14 distinct objects of different sizes, all of which seem to move faster than an electron bubble would be expected to move.

    “They’ve been a mystery ever since they were first detected,” Maris said. “Nobody has a good explanation.”

    Several possibilities have been proposed. The unknown objects could be impurities in the helium—charged particles knocked free from the walls of the container. Another possibility is that the objects could be helium ions — helium atoms that have picked up one or more extra electrons, which produce a negative charge at the detector.

    But Maris and his colleagues, including Nobel laureate and Brown physicist Leon Cooper, believe a new set of experiments puts those explanations to rest.

    New experiments

    The researchers performed a series of electron bubble mobility experiments with much greater sensitivity than previous efforts. They were able to detect all 14 of the objects from previous work, plus four additional objects that appeared frequently over the course of the experiments. But in addition to those 18 objects that showed up frequently, the study revealed countless additional objects that appeared more rarely.

    In effect, Maris says, it appears there aren’t just 18 objects, but an effectively infinite number of them, with a “continuous distribution of sizes” up to the size of the normal electron bubble.

    “That puts a dagger in the idea that these are impurities or helium ions,” Maris said. “It would be hard to imagine that there would be that many impurities, or that many previously unknown helium ions.”

    The only way the researchers can think of to explain the results is through “fission” of the wave function. In certain situations, the researchers surmise, electron wave functions break apart upon entering the liquid, and pieces of the wave function are caught in separate bubbles. Because the bubbles contain less than the full wave function, they’re smaller than normal electron bubbles and therefore move faster.

    In their new paper, Maris and his team lay out a mechanism by which fission could happen that is supported by quantum theory and is in good agreement with the experimental results. The mechanism involves a concept in quantum mechanics known as reflection above the barrier.

    In the case of electrons and helium, it works like this: When an electron hits the surface of the liquid helium, there’s some chance that it will cross into the liquid, and some chance that it will bounce off and carom away. In quantum mechanics, those possibilities are expressed as part of the wave function crossing the barrier, and part of it being reflected. Perhaps the small electron bubbles are formed by the portion of the wave function that goes through the surface. The size of the bubble depends on how much wave function goes through, which would explain the continuous distribution of small electron bubble sizes detected in the experiments.

    The idea that part of the wave function is reflected at a barrier is standard quantum mechanics, Cooper said. “I don’t think anyone would argue with that,” he said. “The non-standard part is that the piece of the wave function that goes through can have a physical effect by influencing the size of the bubble. That is what is radically new here.”

    Further, the researchers propose what happens after the wave function enters the liquid. It’s a bit like putting a droplet of oil in a puddle of water. “Sometime your drop of oil forms one bubble,” Maris said, “Sometimes it forms two, sometimes 100.”

    There are elements within quantum theory that suggest a tendency for the wave function to break up into specific sizes. By Maris’s calculations, the specific sizes one might expect to see correspond roughly to the 18 frequently occurring electron bubble sizes.

    “We think this offers the best explanation for what we see in the experiments,” Maris said. We’ve got this body of data that goes back 40 years. The experiments are not wrong; they’ve been done by multiple people. We have a tradition called Occam’s razor, where we try to come up with the simplest explanation. This, so far as we can tell, is it.”

    But it does raise some interesting questions that sit on the border of science and philosophy. For example, it’s necessary to assume that the helium does not make a measurement of the actual position of the electron. If it did, any bubble found not to contain the electron would, in theory, simply disappear. And that, Maris says, points to one of the deepest mysteries of quantum theory.

    “No one is sure what actually constitutes a measurement. Perhaps physicists can agree that someone with a Ph.D. wearing a white coat sitting in the lab of a famous university can make measurements. But what about somebody who really isn’t sure what they are doing? Is consciousness required? We don’t really know.”

    Authors on the paper in addition to Maris were former Brown postdoctoral researcher Wanchun Wei, graduate student Zhuolin Xie, and George Seidel, professor emeritus of physics.

    See the full article here.

    Welcome to Brown

    Rhode Island Hall: Rhode Island Hall’s classical exterior was recently renovated with a modern interiorRhode Island Hall: Rhode Island Hall’s classical exterior was recently renovated with a modern interior

    Located in historic Providence, Rhode Island and founded in 1764, Brown University is the seventh-oldest college in the United States. Brown is an independent, coeducational Ivy League institution comprising undergraduate and graduate programs, plus the Alpert Medical School, School of Public Health, School of Engineering, and the School of Professional Studies.

    With its talented and motivated student body and accomplished faculty, Brown is a leading research university that maintains a particular commitment to exceptional undergraduate instruction.

    Brown’s vibrant, diverse community consists of 6,000 undergraduates, 2,000 graduate students, 400 medical school students, more than 5,000 summer, visiting and online students, and nearly 700 faculty members. Brown students come from all 50 states and more than 100 countries.

    Undergraduates pursue bachelor’s degrees in more than 70 concentrations, ranging from Egyptology to cognitive neuroscience. Anything’s possible at Brown—the university’s commitment to undergraduate freedom means students must take responsibility as architects of their courses of study.

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  • richardmitnick 3:12 pm on October 17, 2014 Permalink | Reply
    Tags: , , , Quantum Mechanics,   

    From Perimeter: “The Last Gasp of a Black Hole” 

    Perimeter Institute
    Perimeter Institute

    October 17, 2014
    No Writer Credit

    New research from Perimeter shows that two of the strangest features of quantum mechanicsentanglement and negative energy – might be two faces of one coin.

    Quantum mechanics is, notoriously, weird. Take entanglement: when two or more particles are entangled, their states are linked together, no matter how far apart they go.

    If the idea makes your classical mind twitch, you’re in good company. At the heart of everything, according to quantum mechanics, nature has a certain amount of irreducible jitter. Even nothing – the vacuum of space – can jitter, or as physicists say, fluctuate. When it does, a particle and its anti-particle can pop into existence.

    For example, an electron and an anti-electron (these are called positrons) might pop into existence out of the vacuum. We know that they each have a spin of one half, which might be either up or down. We also know that these particles were created from nothing and so, to balance the books, the total spin must add up to zero. Finally, we know that the spin of either particle is not determined until it is measured.

    So suppose the electron and the positron fly apart a few metres or a few light years, and then a physicist comes by to measure the spin of, say, the electron. She discovers that the electron is spin up, and in that moment, the electron becomes spin up. Meanwhile, a few metres or a few light years away, the positron becomes spin down. Instantly. That is the strangeness of quantum entanglement.

    Negative energy is less well known than entanglement, but no less weird. It begins with the idea – perhaps already implied by the positron and electron popping out of nowhere – that empty space is not empty. It is filled with quantum fields, and the energy of those fields can fluctuate a little bit.

    In fact, the energy of these fields can dip under the zero mark, albeit briefly. When that happens, a small region of space can, for a short span of time, weigh less than nothing – or at least less than the vacuum. It’s a little bit like finding dry land below sea level.

    Despite their air of strangeness, entanglement and negative energy are both well-explored topics. But now, new research, published as a Rapid Communication in Physical Review D, is hinting that these two strange phenomena may be linked in a surprising way.

    The work was done by Perimeter postdoctoral fellow Matteo Smerlak and former postdoc Eugenio Bianchi (now on the faculty at Penn State and a Visiting Fellow at Perimeter). “Negative energy and entanglement are two of the most striking features of quantum mechanics,” says Smerlak. “Now, we think they might be two sides of the same coin.”

    ms
    Perimeter Postdoctoral Researcher Matteo Smerlak

    man
    Perimeter Visiting Fellow Eugenio Bianchi

    Specifically, the researchers proved mathematically that any external influence that changes the entanglement of a system in its vacuum state must also produce some amount of negative energy. The reverse, they say, is also true: negative energy densities can never be produced without entanglement being directly affected.

    At the moment, the result only applies to certain quantum fields in two dimensions – to light pulses travelling up and down a thin cable, for instance. And it is with light that the Perimeter researchers hope that their new idea can be directly tested.

    “Some quantum states which have negative energy are known, and one of them is called a ‘squeezed state,’ and they can be produced in the lab, by optical devices called squeezers,” says Smerlak. The squeezers manipulate light to produce an observable pattern of negative energy.

    Remember that Smerlak and Bianchi’s basic argument is that if an external influence affects vacuum entanglement, it will also release some negative energy. In a quantum optics setup, the squeezers are the external influence.

    Experimentalists should be able to look for the correlation between the entanglement patterns and the negative energy densities which this new research predicts. If these results hold up – always a big if in brand new work – and if they can make the difficult leap from two dimensions to the real world, then there will be startling implications for black holes.

    Like optical squeezers, black holes also produce changes in entanglement and energy density. They do this by separating entangled pairs of particles and preferentially selecting the ones with negative energy.

    Remember that the vacuum is full of pairs of particles and antiparticles blinking into existence. Under normal circumstances, they blink out again just as quickly, as the particle and the antiparticle annihilate each other. But just at a black hole’s event horizon, it sometimes happens that one of the particles is sucked in, while the other escapes. The small stream of escaping particles is known as Hawking radiation.

    By emitting such radiation, black holes slowly give up their energy and mass, and eventually disappear. Black hole evaporation, as the process is known, is a hot topic in physics. This new research has the potential to change the way we think about it.

    “In the late stages of the evaporation of a black hole, the energy released from the black hole will turn negative,” says Smerlak. And if a black hole releases negative energy, then its total energy goes up, not down. “It means that the black hole will shrink and shrink and shrink – for zillions of years – but in the end, it will release its negative energy in a gasp before dying. Its mass will briefly go up.”

    Call it the last gasp of a black hole.

    See the full article here.

    About Perimeter

    Perimeter Institute is a leading centre for scientific research, training and educational outreach in foundational theoretical physics. Founded in 1999 in Waterloo, Ontario, Canada, its mission is to advance our understanding of the universe at the most fundamental level, stimulating the breakthroughs that could transform our future. Perimeter also trains the next generation of physicists through innovative programs, and shares the excitement and wonder of science with students, teachers and the general public.

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  • richardmitnick 11:15 am on October 15, 2014 Permalink | Reply
    Tags: , , Loop Quantum Gravity, , Quantum Gravity, Quantum Mechanics, , White Holes   

    From NOVA: “Are White Holes Real?” 

    PBS NOVA

    NOVA

    Tue, 19 Aug 2014
    Maggie McKee

    Sailors have their krakens and their sea serpents. Physicists have white holes: cosmic creatures that straddle the line between tall tale and reality. Yet to be seen in the wild, white holes may be only mathematical monsters. But new research suggests that, if a speculative theory called loop quantum gravity is right, white holes could be real—and we might have already observed them.

    wh

    A white whole is, roughly speaking, the opposite of a black hole. “A black hole is a place where you can go in but you can never escape; a white hole is a place where you can leave but you can never go back,” says Caltech physicist Sean Carroll. “Otherwise, [both share] exactly the same mathematics, exactly the same geometry.” That boils down to a few essential features: a singularity, where mass is squeezed into a point of infinite density, and an event horizon, the invisible “point of no return” first described mathematically by the German physicist Karl Schwarzschild in 1916. For a black hole, the event horizon represents a one-way entrance; for a white hole, it’s exit-only.

    There is excellent evidence that black holes really exist, and astrophysicists have a robust understanding of what it takes to make one. To imagine how a white hole might form, though, we have to go out on a bit of an astronomical limb. One possibility involves a spinning black hole. According to [Albert] Einstein’s general theory of relativity, the rotation smears the singularity into a ring, making it possible in theory to travel through the swirling black hole without being crushed. General relativity’s equations suggest that someone falling into such a black hole could fall through a tunnel in space-time called a wormhole and emerge from a white hole that spits its contents into a different region of space or period of time.

    Though mathematical solutions to those equations exist for white holes, “they’re not realistic,” says Andrew Hamilton, an astrophysicist at the University of Colorado at Boulder. That is because they describe universes that contain only black holes, white holes and wormholes—no matter, radiation or energy. Indeed, previous research, including Hamilton’s, suggests that anything that falls into a spinning black hole will essentially plug up the wormhole, preventing the formation of a passage to a white hole.

    But there’s a light at the end of the wormhole, so to speak. General relativity, from which Hamilton draws his predictions, breaks down at a black hole’s singularity. “The energy density and the curvature become so large that classical gravity is not a good description of what’s happening there,” says Stephen Hsu, a physicist at Michigan State University in East Lansing. Perhaps a more complete model of gravity—one that works as well on the quantum scale as it does on large ones—would negate the instability and allow for white holes, he says.

    Indeed, a unified theory that merges gravity and quantum mechanics is one of the holy grails of contemporary physics. Applying one such theory, loop quantum gravity, to black holes, theorists Hal Haggard and Carlo Rovelli of Aix-Marseille University in France have shown that black holes could metamorphose into white holes via a quantum process. In July, they published their work online.

    Loop quantum gravity proposes that space-time is made up of fundamental building blocks shaped like loops. According to Haggard and Rovelli, the loops’ finite size prevents a dying star from collapsing all the way down into a point of infinite density, and the shrinking object rebounds into a white hole instead. This process may take just a few thousandths of a second, but thanks to the intense gravity involved, the effects of relativity make the transformation appear to take much, much longer to anyone watching from afar. That means that minuscule black holes born in the infant universe could “now be ready to pop off like firecrackers,” forming white holes, according to a report in Nature. Some of the explosions astronomers thought were supernovae may actually be the wails of newborn white holes.

    The black-to-white conversion could resolve a nettlesome conundrum known as the black hole information paradox. The notion that information can be destroyed is anathema in physics, and general relativity says that anything, including information, that falls into a black hole can never escape. These two statements are not at odds if black holes simply act as locked safes for any information they slurp up, but Stephen Hawking showed 40 years ago that black holes actually evaporate over time. That led to the disturbing possibility that the information contained within them could be lost too, triggering a debate that rages to this day.

    But if a black hole instead turns into a white hole, then “all the information is recovered,” says Haggard. “We are quite excited about this mechanism because it avoids so many of the thorny issues that surround this discussion.”

    The new work is preliminary, however, and it is far from clear whether loop quantum gravity is an accurate description of reality. The only glimpse we get of white holes might turn out to be those we model in labs and kitchen sinks. But Carroll says that’s okay. Just thinking about these possibly mythical cosmic creatures can improve physicists’ intuition, “even if the real world is messy and not like those exact situations,” he says. “That’s the way in which white holes are very useful.”

    See the full article here.

    NOVA is the highest rated science series on television and the most watched documentary series on public television. It is also one of television’s most acclaimed series, having won every major television award, most of them many times over.

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  • richardmitnick 3:55 pm on October 3, 2014 Permalink | Reply
    Tags: , , , , Quantum Mechanics   

    From Princeton via Huff Post: “Physicists Observe New Particle That’s Also Its Own ‘Antiparticle'” 

    Princeton University
    Princeton University

    Huffington Post
    10/03/2014
    Macrina Cooper-White

    After decades of searching, physicists at Princeton University say they’ve observed an elusive particle that behaves both like matter and antimatter.

    Yes, the discovery is an exciting step forward for particle physics, but it may also help advance the creation of powerful quantum computers.

    team
    Team not identifed

    In the early 20th century, as quantum theory emerged, scientists predicted that most common particles, like electrons, had mysterious “antimatter” counterparts with the same mass and opposite charge. Scientists even thought that if a particle came in contact with its “antiparticle,” the two would annihilate one another.

    Italian physicist Ettore Majorana first hypothesized in 1937 that one particle — called the “Majorana fermion” — could serve as its very own antimatter particle, and scientists have been searching for that particle ever since.

    iron
    An experiment revealing the atomic structure of an iron wire on a lead surface. The zoomed-in portion of the image depicts the probability of the wire containing the Majorana fermion. The image pinpoints the particle to the end of the wire, which is where it had been predicted to based on years of theoretical calculations.

    For their study, the Princeton researchers designed a simple experiment to observe what they call “emergent particles” which can be found within a material — rather than in the vacuum of a giant collider, where the Higgs boson was discovered.

    “This is more exciting and can actually be practically beneficial,” Ali Yazdani, a physics professor at the university who led the research team, said a written statement, “because it allows scientists to manipulate exotic particles for potential applications, such as quantum computing.”

    The researchers placed a thin, long chain of pure magnetic iron atoms on a superconductor made of lead. Then they cooled the materials to -457 degrees Fahrenheit and peered at them through a two-story-tall scanning-tunneling microscope. Just check out the video above.

    What did the researchers find? An electrically neutral signal at the ends of the iron wires, which is considered to be the “key signature” of the elusive Majorana fermion. The researchers say the fermion’s observed properties make it a good candidate for building quantum bits in computers.

    “One of the first steps in making a quantum computer is to make a quantum bit,” Yazdani said in an email to the Huffington Post, “The ideal quantum bit should [be] one that you can control but it does not interact with its environment, so as to be changed.”

    While other scientists find the study intriguing, many believe further research should be conducted to confirm the results.

    “We should keep in mind possible alternative explanations — even if there are no immediately obvious candidates,” Jason Alicea, a physicist at the California Institute of Technology, who did not participate in this research, told Scientific American.

    The research was published online on Oct. 2 in the journal Science.

    See the full article, with video, here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 9:33 pm on September 25, 2014 Permalink | Reply
    Tags: , , Quantum Mechanics   

    From physicsworld: “Photons weave their way through a triple slit” 

    physicsworld
    physicsworld.com

    Sep 25, 2014
    Hamish Johnston

    A flaw in how quantum-interference experiments are interpreted has been quantified for the first time by a team of physicists in India. Using the “path integral” formulation of quantum mechanics, the team calculated the interference pattern created when electrons or photons travel through a set of three slits. It found that non-classical paths – in which a particle can weave its way through several slits – must be considered along with the conventional quantum superposition of three direct paths (one through each of the slits). The team says the effect should be measurable in experiments involving microwave photons, and that the work could also provide insights into potential sources of decoherence in some quantum-information systems.

    slits
    Road less travelled: a photon weaves its way through three slits

    One of the cornerstones of quantum theory is the fact that particles can also behave as waves. This can be demonstrated by the double-slit experiment with electrons, which was once voted as the most beautiful physics experiment of all time by Physics World readers. It involves firing electrons through two adjacent slits and observing the build-up of a wave-like interference pattern on a screen on the other side of the slits. However, each particle is detected as a tiny dot within the pattern, suggesting that the particles are discrete entities too.

    Physics students are taught that the double-slit pattern can be explained by treating the system as a superposition of waves that travel through one slit and waves that travel through the other slit. Although this description reproduces the pattern seen in experiments, the Japanese physicist Haruichi Yabuki pointed out in 1986 that this approach is approximate because it ignores the tiny possibility that a particle could take a non-classical path through the slits.

    Quantum weaving

    These non-classical paths are easier to think of with an arrangement of three slits. A particle could go through, say, the slit on its left, curve around, go back through the centre slit before turning again and emerging from the slit on the right (see figure). Now, Urbasi Sinha and colleagues at the Raman Research Institute and Indian Institute of Science in Bangalore have calculated the effect of these non-classical paths on the resulting interference pattern of such a triple slit. Using the path-integral formulation of quantum mechanics, the team looked at different combinations of slit width and slit separation for both incident photons and electrons.

    In the case of electrons, the researchers worked out that the non-classical paths would have a minuscule effect on the observed pattern, which would deviate from a simple superposition by a factor of about 10–8. For visible light, this change increases to about 10–5, but this is still too small to detect. Indeed, the calculations explain why Sinha and colleagues at the University of Waterloo in Canada did not see any deviations in an optical triple-slit experiment done in 2010 (see “Quantum theory survives its latest ordeal“).

    Microwaveable deviation

    It turns out, however, that the deviation should rise to about 10–3 for microwave photons, and the team believes that it could be measured in an experiment using photons of wavelength 4 cm, a slit width of 120 cm and a slit separation of 400 cm. Indeed, Sinha told physicsworld.com that her team at the Raman Research Institute has already set up a microwave experiment to look for the effect, but could not comment on the preliminary results.

    Such an experiment, if carried out, could provide a room-sized demonstration of the path-integral formulation of quantum mechanics – something that is normally associated with sub-atomic processes. Furthermore, understanding the role of non-classical paths in interferometer-based quantum-information systems could help physicists reduce the destructive effects of noise in these systems.

    The research is described in Physical Review Letters.

    See the full article here.

    PhysicsWorld is a publication of the Institute of Physics. The Institute of Physics is a leading scientific society. We are a charitable organisation with a worldwide membership of more than 50,000, working together to advance physics education, research and application.

    We engage with policymakers and the general public to develop awareness and understanding of the value of physics and, through IOP Publishing, we are world leaders in professional scientific communications.
    IOP Institute of Physics

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  • richardmitnick 4:41 pm on September 20, 2014 Permalink | Reply
    Tags: , , , , Quantum Mechanics,   

    From Princeton: “‘Solid’ light could compute previously unsolvable problems” 

    Princeton University
    Princeton University

    Sep 08, 2014
    John Sullivan

    Researchers at Princeton University have begun crystallizing light as part of an effort to answer fundamental questions about the physics of matter.

    The researchers are not shining light through crystal – they are transforming light into crystal. As part of an effort to develop exotic materials such as room-temperature superconductors, the researchers have locked together photons, the basic element of light, so that they become fixed in place.

    “It’s something that we have never seen before,” said Andrew Houck, an associate professor of electrical engineering and one of the researchers. “This is a new behavior for light.”

    The results raise intriguing possibilities for a variety of future materials. But the researchers also intend to use the method to address questions about the fundamental study of matter, a field called condensed matter physics.

    “We are interested in exploring – and ultimately controlling and directing – the flow of energy at the atomic level,” said Hakan Türeci, an assistant professor of electrical engineering and a member of the research team. “The goal is to better understand current materials and processes and to evaluate materials that we cannot yet create.”

    The team’s findings, reported online on Sept. 8 in the journal Physical Review X, are part of an effort to answer fundamental questions about atomic behavior by creating a device that can simulate the behavior of subatomic particles. Such a tool could be an invaluable method for answering questions about atoms and molecules that are not answerable even with today’s most advanced computers.

    light

    In part, that is because current computers operate under the rules of classical mechanics, which is a system that describes the everyday world containing things like bowling balls and planets. But the world of atoms and photons obeys the rules of quantum mechanics, which include a number of strange and very counterintuitive features. One of these odd properties is called “entanglement” in which multiple particles become linked and can affect each other over long distances.

    The difference between the quantum and classical rules limits a standard computer’s ability to efficiently study quantum systems. Because the computer operates under classical rules, it simply cannot grapple with many of the features of the quantum world. Scientists have long believed that a computer based on the rules of quantum mechanics could allow them to crack problems that are currently unsolvable. Such a computer could answer the questions about materials that the Princeton team is pursuing, but building a general-purpose quantum computer has proven to be incredibly difficult and requires further research.

    Another approach, which the Princeton team is taking, is to build a system that directly simulates the desired quantum behavior. Although each machine is limited to a single task, it would allow researchers to answer important questions without having to solve some of the more difficult problems involved in creating a general-purpose quantum computer. In a way, it is like answering questions about airplane design by studying a model airplane in a wind tunnel – solving problems with a physical simulation rather than a digital computer.

    In addition to answering questions about currently existing material, the device also could allow physicists to explore fundamental questions about the behavior of matter by mimicking materials that only exist in physicists’ imaginations.

    To build their machine, the researchers created a structure made of superconducting materials that contains 100 billion atoms engineered to act as a single “artificial atom.” They placed the artificial atom close to a superconducting wire containing photons.

    By the rules of quantum mechanics, the photons on the wire inherit some of the properties of the artificial atom – in a sense linking them. Normally photons do not interact with each other, but in this system the researchers are able to create new behavior in which the photons begin to interact in some ways like particles.

    “We have used this blending together of the photons and the atom to artificially devise strong interactions among the photons,” said Darius Sadri, a postdoctoral researcher and one of the authors. “These interactions then lead to completely new collective behavior for light – akin to the phases of matter, like liquids and crystals, studied in condensed matter physics.”

    Türeci said that scientists have explored the nature of light for centuries; discovering that sometimes light behaves like a wave and other times like a particle. In the lab at Princeton, the researchers have engineered a new behavior.

    “Here we set up a situation where light effectively behaves like a particle in the sense that two photons can interact very strongly,” Türeci said. “In one mode of operation, light sloshes back and forth like a liquid; in the other, it freezes.”

    The current device is relatively small, with only two sites where an artificial atom is paired with a superconducting wire. But the researchers say that by expanding the device and the number of interactions, they can increase their ability to simulate more complex systems – growing from the simulation of a single molecule to that of an entire material. In the future, the team plans to build devices with hundreds of sites with which they hope to observe exotic phases of light such as superfluids and insulators.

    “There is a lot of new physics that can be done even with these small systems,” said James Raftery, a graduate student in electrical engineering and one of the authors. “But as we scale up, we will be able to tackle some really interesting questions.”

    Besides Houck, Türeci, Sadri and Raftery, the research team included Sebastian Schmidt, a senior researcher at the Institute for Theoretical Physics at ETH Zurich, Switzerland. Support for the project was provided by: the Eric and Wendy Schmidt Transformative Technology Fund; the National Science Foundation; the David and Lucile Packard Foundation; the U.S. Army Research Office; and the Swiss National Science Foundation.

    See the full article here.

    About Princeton: Overview

    Princeton University is a vibrant community of scholarship and learning that stands in the nation’s service and in the service of all nations. Chartered in 1746, Princeton is the fourth-oldest college in the United States. Princeton is an independent, coeducational, nondenominational institution that provides undergraduate and graduate instruction in the humanities, social sciences, natural sciences and engineering.

    As a world-renowned research university, Princeton seeks to achieve the highest levels of distinction in the discovery and transmission of knowledge and understanding. At the same time, Princeton is distinctive among research universities in its commitment to undergraduate teaching.

    Today, more than 1,100 faculty members instruct approximately 5,200 undergraduate students and 2,600 graduate students. The University’s generous financial aid program ensures that talented students from all economic backgrounds can afford a Princeton education.

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  • richardmitnick 4:25 pm on September 20, 2014 Permalink | Reply
    Tags: , , Quantum Mechanics,   

    From phys.org: “UCI team is first to capture motion of single molecule in real time” 

    physdotorg
    phys.org

    September 16, 2014
    No Writer Credit

    UC Irvine chemists have scored a scientific first: capturing moving images of a single molecule as it vibrates, or “breathes,” and shifts from one quantum state to another.

    aa

    The groundbreaking achievement, led by Ara Apkarian, professor of chemistry, and Eric Potma, associate professor of chemistry, opens a window into the strange realm of quantum mechanics – where nanoscopic bits of matter seemingly defy the logic of classical physics.

    phy
    A simplified view on fields of modern physics theories. Please note that from historical point of view, this diagram is very simplified. In fact, when quantum mechanics was originally formulated, it was applied to models whose correspondence limit was non-relativistic. Many attempts were made to merge quantum mechanics with special relativity with a covariant equation such as the [[w:Dirac equation|Dirac equation]]. In other days, the relativistic quantum mechanics is now abandoned in favour of the quantum theory of fields.

    This could lead to a wide variety of important applications, including lightning-fast quantum computers and uncrackable encryption of private messages. It also moves researchers a step closer to viewing the molecular world in action – being able to see the making and breaking of bonds, which controls biological processes such as enzymatic reactions and cellular dynamics.

    The August issue of Nature Photonics features this breakthrough as its cover story.

    “Our work is the first to capture the motion of one molecule in real time,” Apkarian said. While still images of single molecules have been possible since the 1980s, recording a molecule’s extremely rapid movements had proven elusive.

    In addition to using precisely tuned, ultrafast lasers and microscopes, the researchers had to equip the molecule with a tiny antenna consisting of two gold nanospheres in order to track its activity and record measurements over the course of an hour.

    When the many repeated measurements were averaged, an astonishing finding emerged: The molecule was oscillating from one quantum state to another.

    The scientists have produced a movie in which a small, glowing dot appears to emit pulses of bright light. “That’s the light broadcast from the antenna every time the molecule completes a cycle of its vibrational motion,” Apkarian said. “The bond moves at a rate of 1013 cycles per second – a million, million times 10 cycles in one second.” Making the movie was like freeze-frame photography with a very fast flash and repeating the measurement over and over again.

    Seeing a molecule as it moves is “essential to a deeper understanding of how it forms and breaks chemical bonds,” Potma said. “The aim of the present experiment was to demonstrate that we can capture a molecule in motion on its own timescale.”

    The next and even more ambitious goal is to acquire moving images of molecules in their natural environment without tethering them to an antenna. “Ultimately, we’d like to be able to [examine] a molecule … as it’s undergoing chemistry,” Apkarian said.

    See the full article here.

    About Phys.org in 100 Words

    Phys.org™ (formerly Physorg.com) is a leading web-based science, research and technology news service which covers a full range of topics. These include physics, earth science, medicine, nanotechnology, electronics, space, biology, chemistry, computer sciences, engineering, mathematics and other sciences and technologies. Launched in 2004, Phys.org’s readership has grown steadily to include 1.75 million scientists, researchers, and engineers every month. Phys.org publishes approximately 100 quality articles every day, offering some of the most comprehensive coverage of sci-tech developments world-wide. Quancast 2009 includes Phys.org in its list of the Global Top 2,000 Websites. Phys.org community members enjoy access to many personalized features such as social networking, a personal home page set-up, RSS/XML feeds, article comments and ranking, the ability to save favorite articles, a daily newsletter, and other options.

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